Light Emitting Diode Optical Emitter with Transparent Electrical Connectors

ABSTRACT

An optical emitter includes a Light-Emitting Diode (LED) on a package wafer, transparent insulators, and one or more transparent electrical connectors between the LED die and one or more contact pads on the packaging wafer. The transparent insulators are deposited on the package wafer with LED dies attached using a lithography or a screen printing method. The transparent electrical connectors are deposited using physical vapor deposition, chemical vapor deposition, spin coating, spray coating, or screen printing and may be patterned using a lithography process and etching.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. patentapplication Ser. No. 13/253,797, filed on Oct. 5, 2011, entitled “BackSide Defect Reduction for Back Side Illuminated Image Sensor,” which isa utility patent application of U.S. Provisional Patent Application Ser.No. 61/407,549, filed on Oct. 28, 2010, the disclosures of each of whichare incorporated herein by reference in their entirety.

FIELD

The present disclosure relates generally to a semiconductor light sourceand, more particularly, to a light-emitting diode (LED).

BACKGROUND

A Light-Emitting Diode (LED), as used herein, is a semiconductor lightsource for generating a light at a specified wavelength or a range ofwavelengths. LEDs are traditionally used for indicator lamps, and areincreasingly used for displays. An LED emits light when a voltage isapplied across a p-n junction formed by oppositely doped semiconductorcompound layers. Different wavelengths of light can be generated byvarying the bandgaps of the semiconductor layers (accomplished by, e.g.,using different materials) and by fabricating an active layer (explainedfurther below in the specification) within the p-n junction.Additionally, an optional phosphor material changes the properties oflight generated by the LED.

Traditionally, LEDs are made by growing a plurality of light-emittingstructures on a growth substrate. The light-emitting structures alongwith the underlying growth substrate are separated into individual LEDdies. At some point before or after the separation, electrodes or metalpads are added to each of the LED dies to allow the conduction ofelectricity across the structure. LED dies are then packaged by adding apackage substrate, bonding wires, a reflector, phosphor material, and/orlens to become an optical emitter.

Continued development in LEDs has resulted in light sources that cancover the visible spectrum and beyond. These attributes, coupled withthe potentially long service life of solid state devices, may enable avariety of new display applications, and may place LEDs in a position tocompete with the well entrenched incandescent and fluorescent lamps.

However, improvements in manufacturing processes to make highlyefficient and mechanically robust LEDs continue to be sought.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flowchart illustrating a method of fabricating an opticalemitter according to an embodiment of the present disclosure;

FIGS. 2A-3B are side views and corresponding top views of a partiallyfabricated optical emitter at various stages of fabrication according toan embodiment of the present disclosure;

FIG. 4 is a flowchart illustrating a method of fabricating an opticalemitter according to another embodiment of the present disclosure;

FIGS. 5A-6B are side views and corresponding top views of a partiallyfabricated optical emitter at various stages of fabrication according toanother embodiment of the present disclosure;

FIG. 7 is a flowchart illustrating a method of fabricating an opticalemitter according to another embodiment of the present disclosure; and,

FIGS. 8A and 8B include a side view and a top view of a partiallyfabricated optical emitter according to another embodiment of thepresent disclosure.

SUMMARY

One aspect of the present disclosure involves an optical emitterincluding a Light-Emitting Diode (LED) die, a package wafer attached toone side of the LED die, one or more transparent electrical connectorsconnecting the LED die and at least a contact pad on the package wafer,and a transparent insulator under at least a portion of the transparentelectrical connector. In some embodiments, the optical emitter alsoincludes a Zener diode connected by a transparent electrical connectorto the LED die.

Another aspect of the present disclosure involves a method for forming aplurality of optical emitters on a package wafer. A package wafer isprovided that includes a plurality of Light-Emitting Diode (LED) dieattach areas and a plurality of contact pads, wherein each LED dieattach area is associated with at least one contact pad. The LED diesare attached to the package wafer at the LED die attach areas. Thetransparent insulators are deposited on the package wafer with LED diesattached using a lithography or a screen printing method. Thetransparent electrical connectors are deposited using physical vapordeposition, chemical vapor deposition, spin coating, spray coating, orscreen printing and may be patterned using a lithography process andetching.

These and other features of the present disclosure are discussed belowwith reference to the associated drawings.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of variousembodiments. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed. It isunderstood that various figures have been simplified for a betterunderstanding of the inventive concepts of the present disclosure.Accordingly, it should be noted that additional processes may beprovided before, during, and after the methods described in flowcharts,that some other processes may only be briefly described, and variousprocesses may be substituted for the described processes to achieve thesame effect.

An optical emitter includes an LED die attached to a package substrateand optional phosphor material coating over the LED die or dispersed inencapsulant or lens material. An LED package substrate is usually a leadframe, ceramic, or an alumina board. The LED die may be electricallyconnected to circuitry on the package substrate in a number of ways. Oneconnection method involves attaching a growth substrate side of the dieto the package substrate, and forming metal electrode pads that areconnected to the p-type semiconductor layer and then-type semiconductorlayer in a light-emitting structure on the die, and then bond wiringfrom the metal electrode pads to contact pads on the package substrate.Another connection method involves inverting the LED die and usingsolder bumps to connect the electrode pads on the light-emittingstructure directly to the package substrate. The light from the LED isthen directed through the growth substrate. Yet another connectionmethod involves using hybrid connectors. One semiconductor layer, forexample the p-type layer, may be wired bonded from a metal electrode padto a contact pad on the package substrate while the other layer (n-typelayer) may be soldered to a contact pad on the package substrate.

An optical emitter may be a part of a display or lighting device. Insome configurations, an optical emitter has one or more Light-EmittingDiodes (LEDs), and the LEDs are either controlled individually orcollectively. The optical emitter may also be a part of an integratedcircuit (IC) chip, system on chip (SoC), or portion thereof, that mayinclude various passive and active microelectronic devices such asresistors, capacitors, inductors, diodes, metal-oxide semiconductorfield effect transistors (MOSFETs), complementary metal-oxidesemiconductor (CMOS) transistors, bipolar junction transistors (BJTs),laterally diffused MOS (LDMOS) transistors, high power MOS transistors,or other types of transistors.

A LED die emits light in all directions; however, as a light source, theoptical emitter outputs light only on one side. Thus, an objective of adesigner is to redirect as much of the light emitted in all directionstoward a predetermined light-emitting direction. Further, as much lightas possible is extracted from the die which has a much higher refractiveindex than a lower-index surrounding. Any light that is not properlydirected and extracted may be absorbed and become heat that also needsto be removed. Balanced against light extraction and directionconsiderations are objectives to have good electrical and thermalconduction. In some configurations, the package includes one or moremetal electrode pads and wires in the light path on the output side,which can reduce light extraction by blocking and reflecting the light.For example, a package using metal wires and metal electrodes, which donot transmit any light, can reduced have light output by as much as 20%.In efforts to increase light extraction, smaller metal electrode padshave been used, with the concomitant effect of reducing the reliabilityof the electrical connection and making the wire bonding operation moredifficult. Thinner wires has higher electrical resistance. Wire bondingrequires certain electrode pads to have at least a certain thickness. Toincrease the reliability, a transparent current spreader layer has alsobeen added above the LED die and below the electrode. However, the lightblocking/shielding remains an issue because a metal electrode isrequired to make a wire bond connection.

An optical emitter in accordance with various embodiments of the presentdisclosure uses transparent electrical connectors instead of the metalwire and metal electrode to obtain higher LED light output. The opticalemitter includes a Light-Emitting Diode (LED) die, a package waferattached to one side of the LED die, one or more transparent electricalconnectors connecting the LED die and at least a contact pad on thepackage wafer, and a transparent insulator under at least a portion ofthe transparent electrical connector. As result, the light path from theLED surface is not blocked by any opaque and reflective material such asmetal wires and metal electrodes as it exits the optical emitter.

Two major types of LED dies are the vertical LED die and the horizontalLED die. The main difference between them concerns the direction ofcurrent flow and removal of the growth substrate. In a vertical LED die,the current flows substantially vertically from one side to anotheracross the p-n junction through electrodes located on opposite sides ofthe die. Because the growth substrate is not conductive, it is removedbefore the LED dies are attached to the package wafer. Then one side ofthe LED die is bonded and electrically connected to a LED die attacharea on the package wafer. In this case the attaching may beaccomplished using soldering, metal bonding such as eutectic bonding, orgluing using a conductive glue. The other side of a vertical LED die mayhave one or more wire bonds to the package substrate. For a horizontalLED, the electrical connections for both the p junction and the njunction are made on the same side of the LED die, usually through wirebonding.

Illustrated in FIGS. 1, 4, and 7 are flowcharts of methods 11, 31, and51 of fabricating optical emitters using a wafer level packaging processin accordance with the present disclosure. Corresponding to theflowcharts are diagrammatic fragmentary top and side views of an opticalemitter during various fabrication stages in FIGS. 2A-3B, 5A-6B, and8A-8B, respectively.

Referring to FIG. 1, the method 11 describes various embodiments ofpackaging optical emitters having a vertical LED die. The method 11begins with operation 13 in which a package wafer is provided. A packagewafer may be a silicon wafer, a silicon carbide wafer, or a glass. Inwafer level packaging of LED dies, many LED dies are packaged onto asingle package wafer at the same time. The package wafer includes manyoptical emitter package portions, each package portion includes at leastone LED die attach area and one contact pad. Thus a package waferincludes many LED die attach areas and many contact pads, each contactpad associated with an LED die attach area. Each package portion mayalso include a Zener diode die attach area, another contact pad, andcircuitry either on the package wafer or embedded into the packagewafer. The circuitry may include conductor and/or dielectric patterns(including pads, trenches, and vias), and through vias filled orpartially filled with conductive material. The package wafer may alsoinclude scribe lines, alignment marks, and other features designed forthe optical emitter packaging process. For packaging a vertical LED die,the package portion on the package wafer usually includes only onecontact pad.

In operation 15, LED dies are attached to the package wafer on LED dieattach areas. An LED die includes a light-emitting structure that hastwo doped layers and a multiple quantum well (MQW) layer, also referredto as the active layer, between the doped layers. The doped layers areoppositely doped semiconductor layers. In some embodiments, a firstdoped layer includes an n-type gallium nitride material, and the seconddoped layer includes a p-type material. In other embodiments, the firstdoped layer includes a p-type gallium nitride material, and the seconddoped layer includes an n-type gallium nitride material. The MQW layerincludes alternating (or periodic) layers of active materials including,for example, gallium nitride and indium gallium nitride. For example, inat least one embodiment, the MQW layer includes ten layers of galliumnitride and ten layers of indium gallium nitride, where an indiumgallium nitride layer is formed on a gallium nitride layer, and anothergallium nitride layer is formed on the indium gallium nitride layer, andso on and so forth.

The doped layers and the MQW layer are all formed by epitaxial growthprocesses on a growth substrate, which may be made of silicon, siliconcarbide, gallium nitride, or sapphire. After the completion of theepitaxial growth processes, a p-n junction (or a p-n diode) isessentially formed. When an electrical voltage is applied between thedoped layers, an electrical current flows through the light-emittingstructure, and the MQW layer emits light. The color of the light emittedby the MQW layer is associated with the wavelength of the emittedradiation, which may be tuned by varying the composition and structureof the materials that make up the MQW layer. The light-emittingstructure may optionally include additional layers such as a bufferlayer between the growth substrate and the first doped layer, areflective layer, and an ohmic contact layer. A suitable buffer layermay be made of an undoped material of the first doped layer or othersimilar material. A light-reflecting layer may be a metal, such asaluminum, copper, titanium, silver, silver, alloys of these, orcombinations thereof. An ohmic contact layer may be an indium tin oxide(ITO) layer. The light reflecting layer and ohmic contact layer may beformed by a physical vapor deposition (PVD) process or a chemical vapordeposition (CVD) or other deposition processes.

In operation 17, a patterned transparent insulator is formed over aportion of the LED die and between the LED dies and a contact pad on thepackage wafer. FIGS. 2A and 2B illustrate a side view and a top view ofa package wafer 201, LED die attach area 203, vertical LED die 205, acontact pad 207, and a patterned transparent insulator 209. The crosssection lien for the side view of FIG. 2A is indicated on FIG. 2B asView 2A. The patterned transparent insulator has openings 211 and 213over the LED die 205 and the contact pad 207 respectively. FIG. 2A alsoshows optional through substrate vias (TSVs) 215 and 217. TSVs 215 and217 are filled with a conductor. TSV 215 connects the LED die attacharea 203 to a terminal 219 on the backside of the package wafer 201. TSV217 connects the contact pad 207 to a terminal 221 on the backside ofthe package wafer 201. Note that the TSVs are optional. The opticalemitter may be formed with alternate conductors between the contactpad/LED die attach area and the terminals, for example embedded wiring.

The transparent insulator may be formed by a sequence of processes ofdepositing a transparent insulator layer, patterning the transparentinsulator layer using photolithography methods, and etching thetransparent insulator layer to create an opening over the LED die andthe at least one contact pad. A transparent insulator layer may bedeposited using techniques such as spin-coating, spray-coating,dispensing, molding, dipping, or screen-printing. The transparentinsulator layer covers the entire surface of the LED die 205, contactpad 207 and surrounding the LED die 205 and the contact pad 207.Transparent insulator layer may include a silicone, an epoxy, or apolyimide that do not conduct electricity. The transparent insulatorlayer may not be completely transparent, or allow 100% of the lightgenerated by the LED to pass through; however, the transparent insulatorlayer has a high optical transparency in the visible wavelengths, atleast greater than about 90%, 95%, or 98%.

The transparent insulator layer may be patterned using photolithographymethods. In one example, a photoresist layer is deposited over thetransparent insulator layer and a portion of the photoresist layer isexposed to light. The photoresist layer is then developed to removeportions of the photoresist over the LED die 205 and over the contactpad 207 to form openings above areas where openings 211 and 213 will beformed, respectively.

The photoresist is then used as an etch mask to allow removal of thetransparent insulator layer to form the openings 211 and 213, resultingin the partially fabricated optical emitter as shown in FIGS. 2A and 2B.Although the opening 211 depicted in FIGS. 2A/2B only expose a portionof the LED die 205 and opening 213 depicted in FIGS. 2A/2B only expose aportion of the contact pad 207, the openings 211 and 213 may be largeror smaller.

In some embodiments, the openings 211 and 213 may be patterned to allowbetter electrical conduction. For example, opening 211 may includefingers radiating out of a center portion, or be several interconnectedopenings. The use of photolithographic methods to form openings 211 and213 allow a wide variety of shapes and sizes to be implemented. Theetching process may be a wet etch or a dry etch depending on the type ofphotoresist and transparent insulator layer material used. The etchantis selected to preferentially remove transparent insulator layermaterial as opposed to the etch mask material. After the openings 211and 213 are etched to exposed the underlying LED die 205 and contact pad207, the etch mask is removed in a stripping operation, resulting inpatterned transparent insulator 209.

The patterned transparent insulator may 209 also be formed using ascreen printing process. Screens having desired transparent insulatorpatterns are provided. The screen may be the same size as a packagewafer and can form patterned transparent insulator in one operation forall optical emitters packaged on the same package wafer. In screenprinting, the screen is placed over the package wafer having LED die anda contact pad attached/formed. The screen may be clamped to the packagewafer. A predetermined amount of transparent insulator material is thendispensed in a portion of the screen. A blade or wiper then moves acrossthe screen to spread the transparent insulator material for forming auniform coating. The blade or wiper may make several passes with orwithout adding transparent insulator material. After the transparentinsulator is formed, the screen is removed from the package wafer,resulting in the partially fabricated optical emitter similar to thatshown in FIGS. 2A and 2B.

One difference between a transparent insulator formed usingphotolithographic methods and screen printing methods is the availableshapes of openings 211 and 213. A screen may include a border aroundeach optical emitter package portion, but the stencil for the openings211 and 213 must be connected to the border. Thus openings 211 and 213are either placed along the border of the optical emitter packageportion or include elongate portions that connect the openings to theborder. Further, screen printing is limited in the size of the patternsin the transparent insulator, usually no smaller than the order ofseveral hundred micrometers. Photolithographic techniques can be used toform very small patterns, on the order of several nanometers. However,photolithographic techniques require more processing steps and costmore, both in equipment and material, while the unused transparentinsulator material after screen printing may be recycled. Thus oneskilled in the art may choose one method over another depending on thesize of optical emitter package and transparent insulator patternrequired.

The transparent insulator 209 isolates a transparent electricalconnector from short-circuiting across the LED die. Thus the transparentinsulator is deposited at least in the portion of the optical emitterpackage between the LED die and the contact pad. Particularly, thesidewalls of the LED die are isolated to force all current across thep-n junction.

Referring back to FIG. 1, in operation 19 a transparent electricalconnector is formed. The transparent electrical connector connects aportion of the LED dies not covered by the transparent insulator(through the opening 211) and a contact pad at opening 213. FIGS. 3A and3B depict a side view and a corresponding top of a partially fabricatedoptical emitter with a transparent electrical connector 315 inaccordance with some embodiments. The side view of FIG. 3A shows thecross section at View 3A of FIG. 3B. As shown, transparent electricalconnector 315 covers the entire optical emitter package portion over thetransparent insulator and the openings 211 and 213. Because theunderlying transparent insulator isolates LED die, the transparentelectrical connector 315 can be deposited in one operation withoutpatterning.

The transparent electrical connector 315 is highly conductive andoptically transmissive in the visible wavelengths. While completetransparency is not required, the transparent electrical connector 315allows most of the light to pass through, at least greater than about90%, 95%, or 98%. Suitable material includes inorganic and organicmaterials. Example inorganic materials include indium tin oxide (ITO),any other transparent conductive metal oxides, or inorganic conductiveglue. Example organic materials include epoxy, resin, polyimide, orother polymer that further includes a conductive additive such as metalparticles or carbon particles. In one example, the conductive glue is anepoxy with fine silver particle additives. As the conductive glue dries,the silver particles form a conductive network. The concentration andtype of conductive particles in the glue and thickness of the depositedconductive glue layer affects the conductivity of the electricalconnector. For optical emitters containing high power LEDs, conductiveglue with sufficient conductivity should be chosen to avoid reliabilityproblems.

The transparent electrical connector 315 of FIGS. 3A and 3B is anunpatterned transparent conductive layer. Because the LED die isconnected to only one contact pad, only one electrical connector isused, which can be an entire layer. A transparent conductive layer maybe deposited using known techniques such as physical vapor deposition(PVD), chemical vapor deposition (CVD), spin-coating, spray-coating,dispensing, molding, dipping, and screen-printing. Other embodimentsinvolve multiple transparent electrical connectors formed using othermethods as discussed below.

Referring back to FIG. 1, a top surface of the transparent insulatorlayer and the transparent electrical connector may be optionally maderough in operation 21 after the transparent electrical connector ismade. A rough surface improves light extraction because total internalreflection is less likely with many faceted surfaces. The roughing maybe performed by exposing the package wafer to plasma etching, wetetching, or depositing small transparent particles on the top surface.

Next, the optical emitter packaging may further include the addition ofa number of optional components added onto the package wafer. One ormore layers of phosphor may be added to the package to change theemitted light wavelength. One or more layers of encapsulant or lens maybe formed over the LED die. Side reflectors may also be added for eachoptical emitter to redirect side light emissions. Some of theseadditional components may be formed in combination. For example, thephosphor material may be a part of the lens or be coated onto the lens.Some of these additional components may be omitted. For example, sidereflectors may not be needed for optical emitters containing certainvertical LEDs.

After optical emitter packaging is completed on the package wafer, thepackage wafer is optionally diced into a number of optical emitters inoperation 23 along boundaries of optical emitter package portions. Thepackage wafer may be cut through transparent insulator layers andtransparent conductive layers by a saw or laser.

The optical emitter with vertical LED described in association withFIGS. 1-3B has improved light output as compared to conventional opticalemitters because no opaque material such as metal wires and electrodesare placed in the output light path. The resulting optical emitter isrobust because no flexible wires are used and can withstand mechanicalpressure better in subsequent processing. The fabrication process isrelatively simple and requires only uncomplicated process tools, forexample, screen printer and spin coater. The transparent electricalconnector being an entire transparent conductive layer ensures a betterelectrical connection than point-to-point wire bonding. In someembodiments such as high-end optical emitters, complicated patterns forelectrical connectors are formed by using photolithographic processes.One or more of these features apply to embodiments of the presentdisclosure.

FIG. 4 is a flowchart of an optical emitter with horizontal LED inaccordance with various embodiments of the present disclosure. FIGS. 5Aand 6A are side views of an optical emitter at various fabricationstages according to some embodiments, and FIGS. 5B and 6B are top viewscorresponding to FIGS. 5A and 6A, respectively. The remaining discussionfocuses on the differences from embodiments depicted in FIGS. 1-3B, andsimilar details are not repeated. FIG. 5A shows a horizontal LED die 503including the growth substrate 505, a first doped layer 507 above thegrowth substrate 505, multiple quantum wells (MQWs) 509 on the firstdoped layer 507, and a second doped layer 511 formed on the MQWs 509.The second doped layer 511 is oppositely doped from the first dopedlayer 507. FIG. 5A shows the side view from two separation sections ofFIG. 5B as shown.

The method 31 illustrated in FIG. 4 includes some process operationssimilar to that of FIG. 1. In operation 33, a package wafer is provided.As shown in FIG. 5A, the package wafer 501 includes an LED attachmentarea 513, contact pads 515 and 517 for electrically connecting to thefirst doped layer 507 and second doped layer 511, respectively, andthrough substrate vias (TSVs) 519 and 521 filled at least partially witha conductor, which electrically connects the front side of the packagewafer 501 to terminals on the backside of the package wafer. Similar tothe package wafer 201 of FIG. 2, the TSVs shown in FIG. 5A are notrequired in some embodiments.

Referring to FIG. 4, in operation 35, LED dies are attached to thepackage wafer on the LED die attach area. Referring to FIGS. 5A and 5B,the LED die 503 is attached to package wafer 501 on an LED die attacharea 513. In these embodiments, the attachment of the LED die 503 to thepackage wafer 501 is a non-conductive connection because the sapphiresubstrate 505 is non-conductive. In some embodiments, the sapphiresubstrate is removed prior to attaching the LED die, and the LED diedoes not include the sapphire substrate 505. In the embodiments withouta sapphire substrate, the attachment to the package wafer 501 isnon-conductive.

In operation 37, a patterned transparent insulator is formed over aportion of the LED die and between the LED dies and two contact pads onthe package wafer. Referring to FIGS. 5A and 5B, the patternedtransparent insulator 523 includes various openings 525, 527, 529, and531 for subsequent formation of transparent electrical connectors. Thepatterned transparent insulator 523 and openings 525, 527, 529, and 531are formed substantially the same as the formation of patternedtransparent insulator 209 and openings as discussed above in associationwith FIGS. 1 and 2A/2B.

Referring back to FIG. 4, in operation 49 transparent electricalconnectors are formed. The transparent electrical connectors connect aportion of the LED dies without the transparent insulator (openings 527and 529) and contact pads at openings 525 and 531, respectively. Thetransparent electrical connector may be formed by a sequence ofprocesses of depositing a transparent conductive layer, patterning thetransparent conductive layer using photolithography methods, and etchingthe transparent conductive layer to create one or more electricalconnectors over the LED die and the at least one contact pad. Atransparent conductive layer may be deposited using known techniquessuch as physical vapor deposition (PVD), chemical vapor deposition(CVD), spin-coating, spray-coating, dispensing, molding, dipping, andscreen-printing. Because there are two separate transparent electricalconnectors 601 and 603, the transparent conductive layer is patterned.The transparent conductive layer may be patterned using photolithographymethods. In one example, a photoresist layer is deposited over thetransparent conductive layer and a portion of the photoresist layer isexposed to light. The photoresist layer is then developed to exposeportions of the transparent conductive layer that would make a shortcircuit around the LED die. The remaining photoresist then acts as anetch mask in a subsequent etching process where the exposed portions ofthe transparent conductive layer is removed. The etching process may bea wet etch or a dry etch, depending on the material used as thetransparent conductive layer. After the etch is completed, the remainingphotoresist may be removed in a stripping process. While FIG. 6B showsthat transparent electrical connectors 601 and 603 occupy a small areacomparing to the transparent insulator, the transparent electricalconnectors 601 and 603 can be of any shape and area as long as the twoelectrical connectors 601 and 603 are electrically isolated from eachother.

The patterned transparent electrical connectors may also be formed usinga screen printing process. Screens having desired transparent electricalconnector patterns are provided. The screen may be the same size as apackage wafer and can form patterned translator electrical connector inone operation for all optical emitters packaged on the same packagewafer. The screen printing operation is similar to that described abovein association with screen printing a transparent insulator inassociation with operation 17 of FIG. 1.

The remaining optional operations 41 and 43 are the same as operations21 and 23 of FIG. 1 describe above and are not repeated.

FIG. 7 is a flowchart of fabricating an optical emitter with a Zenerdiode die in accordance with various embodiments of the presentdisclosure. FIGS. 8A and 8B depict a side view and a corresponding topview of a partially fabricated optical emitter in accordance with someembodiments. FIG. 8A shows the side view from two separation sections ofFIG. 8B as shown. In these embodiments, the LED die is packaged with anelectro-static discharge (ESD) and/or electrical fast transient (EFT)protection circuit such as a Zener diode die. In some embodiments, othercommonly used ESD and EFT protection devices are used, such as atransient suppression diode and a multilayer varistor. When packaged inclose proximity to the LED die, the wiring connections for ESD and EFTprotection circuitries become a part of the optic system, often blockingor shielding the light. Thus in these embodiments, a transparentelectrical connector electrically connects the Zener diode die to theLED die and the electrical connector between a contact pad on thepackage wafer and the Zener diode die may be another transparentelectrical connector or an embedded metal connector on or in the packagewafer.

The operations in the process flow of FIG. 7 are similar to theoperations in the process flow of FIGS. 1 and 4 with the exception ofadditionally attaching Zener diode dies to the package wafer on Zenerdiode die attach areas in operation 57, forming a patterned transparentinsulator between the LED dies and the Zener diode dies in operation 59,and forming a transparent electrical connector between an exposedportion of the LED dies and Zener diode dies in operation 61.

FIGS. 8A and 8B illustrate one embodiment of the transparent insulator801 and transparent electrical connectors 803, 805, and 807 for anoptical emitter with a Zener diode die. The transparent insulator 801and transparent electrical connectors 803, 805, and 807 are formed withprocesses as explained above but with different patterns to allow theadditional electrical connector for the Zener diode 809.

Note that while transparent insulators and electrical connectors areillustrated with right-angled comers and uniform thicknesses, inpractice the various processing may result in various types ofconfigurations for the transparent insulators and electrical connectors,e.g., less defined corners and different thicknesses. For example, theopenings 211 and 213 may be completely filled by the transparentelectrical connector 315 instead of being conformally coated as shown inFIG. 3A.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein. Forexample, additional transparent electrical connectors may be formed toconnect additional circuitry, (i.e., driver, controller, IC chip) to theLED die. In other examples, a network of transparent electricalconnectors may connect multiple LEDs on one optical emitter. Thoseskilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A method of fabricating an optical emitter, comprising: providing apackage substrate that includes a die-attach area and a contact pad, thedie-attach area being spaced apart from the contact pad; attaching alight-emitting diode (LED) die to the die-attach area, the LED diecontaining a vertical LED; forming a patterned transparent insulatinglayer over the package substrate and over the LED die and the contactpad, wherein at least a portion of the patterned transparent insulatinglayer separates the LED die and the contact pad, and wherein thetransparent insulating layer includes a first opening exposing a portionof the LED die and a second opening exposing a portion of the contactpad; and forming a transparent electrical conductor over the patternedtransparent insulating layer such that the first opening and the secondopening are each at least partially filled with the transparentelectrical conductor, thereby electrically coupling the LED die with thecontact pad.
 2. The method of claim 1, wherein the forming of thepatterned transparent insulating layer comprises: depositing atransparent insulating material over the package substrate and over theLED die and the contact pad; and etching the transparent insulatingmaterial to form the first opening and the second opening.
 3. The methodof claim 1, wherein the forming of the patterned transparent insulatinglayer is performed via a screen printing process.
 4. The method of claim1, wherein the providing the package substrate comprises forming a firstthrough-substrate via (TSV) and a second TSV, the first TSV beingelectrically coupled to the die-attach area, and the second TSV beingelectrically coupled to the contact pad.
 5. The method of claim 1,further comprising: roughening a surface of the patterned transparentinsulating layer and a surface of the transparent electrical conductor.6. A method of fabricating an optical emitter, comprising: providing apackage substrate that includes a die-attach area, a first contact pad,and a second contact pad, the die-attach area being spaced apart fromthe first and second contact pads; attaching a light-emitting diode(LED) die to the die-attach area, the LED die containing a horizontalLED that includes an n-type doped layer, a p-type doped layer, and alight-emitting layer disposed between the n-type doped layer and thep-type doped layer; forming a patterned transparent insulating layerover the package substrate, the LED die, and the first and secondcontact pads, wherein the patterned transparent insulating layerseparates the LED die from the first and second contact pads, andwherein the transparent insulating layer includes first, second, third,and fourth openings, the first and second openings exposing the n-typedoped layer and the p-type doped layer of the horizontal, respectively,the third and fourth openings exposing the first and second contactpads, respectively; and forming a patterned transparent electricalconductor layer over the patterned transparent insulating layer suchthat the first and third openings are each at least partially filledwith a first segment of the patterned transparent electrical conductorlayer, thereby electrically coupling the n-type doped layer with thefirst contact pad, and the second and fourth openings are each at leastpartially filled with a second segment of the patterned transparentelectrical conductor layer, thereby electrically coupling the p-typedoped layer with the second contact pad, and wherein the first andsecond segments of the patterned transparent electrical conductor layerare formed to be electrically isolated from one another.
 7. The methodof claim 1, wherein the forming of the patterned transparent insulatinglayer comprises: depositing a transparent insulating material over thepackage substrate and over the LED die and the first and second contactpads; and etching the transparent insulating material to form the first,second, third, and fourth openings.
 8. The method of claim 1, whereinthe forming of the patterned transparent insulating layer or the formingof the patterned transparent electrical conductor layer comprises ascreen printing process.
 9. The method of claim 1, wherein the providingthe package substrate comprises forming a first through-substrate via(TSV) and a second TSV, the first TSV being electrically coupled to thefirst contact pad, and the second TSV being electrically coupled to thesecond contact pad.
 10. The method of claim 1, further comprising:roughening a surface of the patterned transparent insulating layer and asurface of the patterned transparent electrical conductor layer.
 11. Amethod of fabricating a plurality of optical emitters, comprising:providing a package wafer having a plurality of Light-Emitting Diode(LED) die attach areas and a plurality of contact pads, wherein each LEDdie attach area is associated with at least one contact pad; attaching aplurality of LED dies to the package wafer at the plurality of LED dieattach areas; forming a transparent insulator between each of pluralityof LED dies and the at least one contact pad associated with the LED dieattach area; and, forming a transparent electrical connector betweeneach of plurality of LED dies and an associated contact pad.
 12. Themethod of claim 11, wherein the forming a transparent insulatorcomprises: depositing a transparent insulator layer, patterning thetransparent insulator layer, and etching the transparent insulator layerto create an opening over the LED die and the at least one contact pad.13. The method of claim 11, wherein the forming a transparent insulatorcomprises screen printing a patterned transparent insulator.
 14. Themethod of claim 11, wherein the forming a transparent electricalconnector comprises: depositing a transparent conductive layer,patterning a photoresist over the transparent conductive layer, andetching the transparent conductive layer through the pattern down to thetransparent insulator layer.
 15. The method of claim 14, wherein thedepositing a transparent conductive layer comprises depositing usingphysical vapor deposition, depositing using chemical vapor deposition,spin coating, or spray coating.
 16. The method of claim 14, wherein theetching is wet etching.
 17. The method of claim 11, wherein the forminga transparent electrical connector comprises screen printing atransparent electrical connector.
 18. The method of claim 11, whereinthe at least one contact pad is two contact pads and further comprisingforming another transparent electrical connector electrically connectingeach of the plurality of LED dies and a second associated contact pad.19. The method of claim 11, further comprising dicing the package waferinto a plurality of optical emitters.
 20. The method of claim 11,further comprising roughing a top surface of the transparent insulatorlayer and the transparent electrical connector.